Every person who constructs a new dwelling, makes additions in habitable space to any existing dwelling, or improves land as a mobile home shall be subject to a construction tax. Pursuant to Municipal Code Sec. 5-1204.1, Construction Tax, Ordinance No. 1876, approved at an election held June 6, 1989, the Finance Director shall set the annual rates effective July 1 of each year based on the change in the gross national product (GNP) deflator.